[Q] Question about google play music

I want to keep specific songs from different albums on my device for offline play, but i cant figure out how to do it, if its at all possible.

When i go to my library on my nexus 4 i can press the menu button on an album and keep on device but if i go over to the right to songs to see all the individual songs and press the menu button i dont have the option to keep individual songs on the device.

Can someone tell me if its possible? And if so how?

Thanks peeps.